Volume control device for electron tube systems



Feb, 5, 1935. G. E. FLEMING 1,989,797

VOLUME CONTROL DEVICE FOR ELECTRON TUBE SYSTEMS Filed Feb. 20, 1951 2 Sheets-Sheet 1 II II $51 150 Guam m Ge orge E H e172 2729 G. E. FLEMING 11,989,797

VOLUME CONTROL DEVICE FOR ELECTRON TUBE SYSTEMS Feb. 5, 1935.

2 Sheets-Sheet 2 Filed Feb. 20, 1951 Ewuemtoz George Zflemzrzg 154/ GM @1 W ma Patented Feb. 5, 1935 UNITED STATES PATENT OFFICE VQLUME CONTROL DEVICE FOR ELECTRON TUBE SYSTEMS 10 Claims.

- This invention relates to a novel method of and apparatus for controlling the volume or output intensity of electron tube systems and, in particular, to anautcmatic control for maintaining the output of such systems substantially constant or otherwise under desired control, while the intensity of the incoming signal energy varies.

Various methods and devices have been proposed and used, heretofore, for accomplishing volume control in radio receiving and similar electron tube systems. While some of these prior designs have to rely upon the addition of auxiliary electron tubes to the system, in other cases attempt has been made to accomplish the desired results by introducing a resistance with sliding contact or by providing means for changing the biasing potential of a tube in the system. None of these procedures is free from serious drawbacks. Sliding contacts are objectionable since, in course of time, their character changes; they are also likely to create objectionable noise disturbances in systems with telephone or loudspeaker output. Changing tube biasing potentials in such systems is frequently accompanied by an impairment of the overall efficiency and faithfulness of reproduction.

The object of this invention is to provide in an electric signal energy transmitting system including an electron tube system, a volume control, either manual or automatic, of simple and inexpensive character and based on the principle of deriving variable difierential signal voltages from an adjustable impedance combination, inserted in some section of the system or being part of it, and transferring these controllable differential voltages to a succeeding section of the system.

Special features of my arrangement are its substantial freedom from injurious influences on the operating characteristics of the system and the possibility of avoiding sliding contacts for controlling purposes.

Furthermore, the volume control devices of this invention, non-automatic and automatic, are particularly adapted to be assembled in a self-contained, compact unit with a few exteriorly accessible terminals for convenient insertion in any radio receiving or similar system irrespective of the special operating or construction features of such system. Still other objects and advantages will be pointed out in the subsequent description with reference to the drawings, in which Fig. 1 shows a preferred wiring scheme for manual control with all requisite control elements connected between the antenna and the radio receiving set, the latter being indicated only symbolically;

Fig. 2 shows the complete wiring diagram of an alternating current energized, two-tube highfrequency receiving system, including one stage of radio frequency amplification and a detector stage with the control elements in interstage connection;

Fig- 3 shows in vertical section an equipment for automatic control comprising a motor or galvanometer coupled to a variable condenser with all requisites assembled in a casing;

Fig. 4 is a horizontal section substantially on line AA of the device of Fig. 3; and

Fig. 5 is a fractional horizontal section taken partly on line B-l3 and partly on line B--B of Fig. 3.

With reference to Fig. .1 it will be noted that the signal energy-21. modulated or non-modulated carrier waveis received on the antenna A and transmitted by way of terminal ii of the antenna and terminal t2 of the grounding structure G through two circuits each including a variable condenser C1 and C2 respectively and a coupling coil L1 and L2 respectively. Though there are shown two coils, one coil with intermediate winding connection to terminal t1 may be used. The coils L1 and L2 are inductively coupled with coil L3, whose terminals t3 and t4 are directly joined to the input terminals 125 and is of the radio receiving set R S. The latter may be a system of any kind adapted to receive and transmit or, in addition, translate radio signals.

The system may be termed an impedance bridge, since, by bridging two points of the parallel impedance circuits, a differential potential is obtained formed by the differences of potential of the two bridging points with respect to a constant level potential, such as the ground potential of the lower antenna portion. The value of this differential voltage may be changed by changing the impedance of one of the branches of the impedance combination. In providing a coupling of conductive or reactive nature, common to both branches of the bridge, energy may be transferred from the bridge to a succeeding section of the electric system in amounts varying between zero value and a maximum value determined by the highest degree of unbalance that can be established with respect to zero transfer condition. Instead of forming the difference of potentials in the impedance systemitself this difference may also be obtained in the coupling means as when two coils, each belonging to another of two multiple circuits in the impedance system are each coupled in proper phase relation with a separate coil connected in multiple in a succeeding portion of the transmitting system.

As illustrated in Fig. 1 I prefer using coils of fixed inductance values for coupling the bridge with the succeeding section the system and two variable condensers for changing the degree of unbalance in the bridge arrangement. I may, however, content myself with providing two condensers of. which only one is variable and, in point of fact, I have found that with such simplified arrangement I can obtain a perfectly satisfactory range of variability; If with anincoming signal, say of medium strength, the operator has adjusted the capacitance for the desired intensity of transfer or translation, can maintain this intensity level for signals weaker and stronger as well as the one for which the original adjustment was made by increasing or decreasing respectively the originally established unbalance.

The advantages of this control arrangement over devices with variable resistance elements are obvious; @The absence of resistance elements increases the overall efliciency and selectivity of the system. The electric contact with the movable element of the condenser can be made of a nature insuring perfect stability, that is uniform resistance, under all operating conditions. Preferably, I use a flexible wire for this purpose. The variation of signal intensity in my arrangement follows a smooth curve for all operating conditions.

It is evident that I may use variable inductances instead of variable condensers. Furthermore, the two non-variable inductive couplings may be replaced by either capacitive or resistive couplings in combination with capacitive or inductive vari'- able impedance elements; Finally,.variable .inductive impedance elements may be used to function, at the same time, as coupling elements.

It will be understood that, instead of inserting the-control element'sbetween the signal supply structure, to the "system-antenna, phonographic pick-up, etc.-.they may also be inserted between may be an audio-frequency tube system or a trans- Also, coil Ls controlled. I

In assembling all parts included in-the, dotted frame of Fig. 1 in a separate casingjI am in a position to provide an effective shielding between the elements of the control system and those of thesystem proper and to put in the hands of the radio amateur a compact control device exhibiting nothing but one or two adjusting knobs and four binding posts whose proper connection is an easy matter.

In Fig. 2 the control arrangement is shown in interstage connection and in combination with an automatic governor device. With reference to this figure it will be noted that, by way of example, I have illustrated an electron tube system energized from alternating current, say a house lighting system, by way of plug terminals S1, Sz-and transformer Ts. Two secondary coils of this transformer-are used to operate the rectifier R, while a third secondary serves to heat the tube filaments; F is a conventional filter systerm as employed in conjunction with alternating currentenergization. The input of the tube systemis shown symbolically at I and may be any suitable structurefor supplying signal energy to the tube system. V1 isa high-frequency amplifier tube with four electrodes and indirectly heated cathode; a three-electrode tube may, of course, be substituted for it. The grid of this tube receives signal energy, by way of the circuit including I and by-pass condenser C and is biased through the circuit including I and biasing resistance R1. The screen-grid is energized with an intermediate potential obtained from the positive side of the source by the interposition of "resistance R3. The plate electrode of the tube is energized by way of coil L0. The potential difference between the terminals of this coil is utilized to energize the impedance bridge of the control system which is shown comprising the same elements as the previously described system of Fig. 1, that is, two variable condensers C1 and C2 and two coils L1 and L2 of fixed values and both linked with coil L3 which latter forms the impedance 0 which may be a low frequency tube system, a;

loud-speaker or any other suitable structure.

As will be seen, the output circuit of the detector. tube V2 includes, besides the primary coil L4 of the transformer To, a small motor M with its terminals put on a potentiometer resistance Rp. This resistance serves to adapt the motor characteristic to different current intensities in different systems or different; sections of the same system and is not, otherwise, anecessary func tional element in the control system. This motor, .a preferred design of which will be described later on, is mechanically coupled to the variable condenser C1 of the control system and has an armature which, under the influence of varying energization current, will provide a correspondingly varying torque at the motor shaft for displacing the movable condenser element of condenser C1; For instance, with increasing signal tensity the control system will be governed towards increasing balance of its impedance elements resulting in a decrease of the amount of energy transferred to the succeeding detector stage and, finally, in the establishment of a new dynamic balance in accordance. with the increased strength of the received signal. The mechanical coupling between the motor armat re and'the condenser has been indicated in the figure by a connecting link between the two arrows representing the respective movable elements. v v

The capacitance of the variable condenser C2 may be manually controllable. ting of the capacitance value of this condenser may be done in like manner as ekplainedin connection with the arrangement of Fig. 1. this setting has been made according to the operators preference, the output of the system will, within certain variations above and below the value selected by adjusting the manually operable condenser, remain at substantially constant level.

The operation of this system under diiferent circumstances in the transmitting system will be better understood with reference to Figs. 3 to 5. These figures illustrate a specific embodiment of the motor-condenser arrangement,

As. shown in Figs. 3 and 4 the condenser plates are. housed at the bottom of easing 1 which is Tube The initial set- .After 1,989,797 ,made from some sort' of insulating. material.

These plates are sector-shaped and extend each through an angle of about 90 degrees. The movable element comprising sectors 4, 4 is mounted on a shaft 5 having a lower and upper bearing 6 and 7 respectively. A flexible, so-called pig-tail wire 11 connects this shaft with the binding post 27 thus permitting the electric connection of the movable element by means of a permanent contact. The stationary condenser element consists of a pair of lower sectors 3, 3' and a pair of upper sectors 2, 2. The two lower sectors are, preferably, cut integrally from a piece of metal sheet leaving a central apertured connecting portion 3' (see Fig- 4) between the two sectors, while the upper sectors are separate metal sheets conductively connected with the lower plates and with each other through the bolt joints 33. The electric connection for this stationary element can be made at post 28.

Mounted on shaft 5 is a little permanent bar magnet 8 (see Figs. 3 and 5). This bar magnet assumes-diiferent positions under the influence of two opposing torques, the one exerted by the horse-shoe magnet 10 and the other by the electromagnet 20. The electromagnet or coil 20' is fastened to a portion of the casing wall by means of bracket 16 and may be energized by way of the two binding posts 25 and 26. This energization of the coil may take place from any portion in the signal transmitting system whose steady component current conditions are modified with varying signal strength. Normally, the bar, magnet, under the influence of the field of the horse-shoe maget, is held in the position shown in Fig. 5, but, as the current in the coil increases, the bar magnet will tend to orient itself in the direction of the axis of the coil, the interior space of which is wide enough to accommodate the deflected magnet. The apparatus works on the galvanometer principle, and, for this reason, I shall subsequently frequently refer to it by the term of galvanometer-condenser.

The position of the horse-shoe magnet may be adjusted vertically and angularly with respect to the bar magnet by means of a rod 12 joined to the horse-shoe magnet through cross bars 11 and. axially and rotatably movably held between an elastic sleeve 13, the desired position being selected by grasping knob 15 and secured by screwing down nut 14 on the external, conical thread of sleeve 13.

With the disposition of elements as shown in the figures the capacity of the condenser will be lowest, say about zero, with no current flowing in the coil. The normal current for energizing the electronic path of the circuit in which the galvanometer-condenser is inserted will deflect the bar magnet a certain amount. In turning thev horse-shoe magnet about its rod axis, this deflection may be more or less compensated thus permitting the setting of the magnetic system on a desired zero position for normal energizetion current. With an incoming signal, say, of medium strength, and the manually controllable condenser C2 of Fig. 2 adjusted for a desired intensity of translation the galvanometer current will increase due to detection effects in the system and the capacity of the galvanometercondenser will accordingly assume an intermediate value. For a final setting potentiometer resistance Rp could also be used.

Signals above medium strength will, then, tend to further increase the capacity of the galvanometer-eondenser and, thereby, depress the signal strength towards medium level,'while signals below medium level will decrease the capacity and thus raise the signal strength towards the desired value. In the case of grid-current detection the relation between changing signal strength and change of steady-component current is reversed. In this case, it is only necessary to modify the disposition of the elements in the galvanometer-condenser so as to give maximum capacity at zero position. To meet these contrary conditions with the same control device the position of the stationary condenser element may be made adjustable as illustrated in Figs. 3 and 4. The lower extremities of the bolts 33 engage in an annular groove of a rail 30. By grasping the handle 32 protruding through a slot in the casing the stationary condenser element may be turned through an angle permitting of a registering adjustment of the stationary and movable plates with attendant maximum capacity. For holding the stationary element, when turning the same, at accurate spacing from the movable element depressing springs as shown at 31 are provided.

Due to the vertical and angular adjustability of the horse-show magnet, its torque on the bar magnet may be changed both as to magnitude and distribution about the axis of the bar magnet, thus permitting the selection of suitable values for given operating conditions. It is, furthermore, obvious that by providing poles on the horse shoe magnet other than shown-the distribution of the magnetic field may be given almost any desired form. Such expedients are well known to the experts of the art.

It will be understood that I may resort to one or the other of the various adjusting means or may use several in combination as shown in the drawings. Also, instead of making the outfit adaptable for operation with either plate or grid detection, I may have a design arranged only for the one or other mode of operation. A great many other modifications may, of course, be made without departing from the spirit of the invention. For instance, the permanent magnets could be replaced by elcctromagnets, the condensers by inductances, the torque produced by the horse-shoe magnet by a mechanically produced torque as from a twisted cord, a twisted helical spring or the like.

The coil circuit of the galvanometer may be inserted in any circuit portion with sufficient detection effects of a complex system comprising a signal supply structure, a high-irequency amplification stage, a detection stage, a low-frequency amplification and an output receiving structure. There may be come liability of the instrument of being over-sensitive and falling into oscillations of its natural frequency tending to produce audible disturbances in the system. For this reason, I provide suflicient damping in the device, which in association with electrical advantages is very efiectively obtained in the form of windage through closely spacing the stationary and movable condenser plates. The moment of inertia of the movable elements of the galvanometer-condenser can easily be selected to prevent an undesirable responsiveness of the instrument to audio frequencies.

It will be understood that, besides the galvanometer and condenser, also the coupling impedances may be housed in the same casing thus providing a self-contained control equipment which may be used as an accessory or supplemental outfit in combination with any signal transmitting system-having sufiicient detection effects in one of its portions or permitting deriving from it such detection effects with any convenient means. I

In the preceding description I have, for'the purpose of exemplification, referred to specific transmitting systems and specific embodiments of my. invention without intending to limitthe scope of my invention as defined in the appended claims.

.I claim:

' 1. In an electric system for transferring signal energy including an electron-tube system, the combination of a plurality of impedance circuits connected in multiple to a preceding portion in said electric system and including at least one variable, substantially reactive impedance, coupling means between said plurality of impedance circuits and a succeeding portion of said system for obtaining differential signal voltages therein, said coupling means having such electrical proportions and coupling relations with respect to each other and the said succeeding portion of the system that for one value of said variable impedance within its range of variation the transferred diiferential signal voltages substantially neutralize, and adjusting means for said variable impedance, whereby the signal energy transferred tosaid succeeding portion maybe varied from substantially no value to various desired finite values.

2. In an electric system for transferring signal energy including an electron-tube system, the combination of two impedance circuits connected in multiple to a preceding portion in said electricsystem, each circuit including a condenser and a coil with at least one of said condensers having a variable capacitance, an inductive coupling between said coils and a coil in a succeeding portion of the system for transferring differential signal voltages thereto, and adjusting means for said variable condenser, whereby with varying signal strength the succeedingly transferred signal strength may be controlled.

i .3. In an electric system for transferring signal energy including an electron-tube system and a structure for'supplying signal energy thereto, the combination of two impedance circuits connected in multiple to said signal supply structure, each circuit including a condenser and a coil with at least one of said condensers having a variable capacitance, an inductive coupling between said coils and a coil in said electron tube system for transferring differential signal voltages thereto, and adjusting means for said variable condenser, whereby with varying signal strength in said supply structure the siganl strength transferred to said electron-tube system may be controlled.

4. In an electric system for transferring signal energy including an electron-tube system, the combination of a plurality of impedance circuits connected in multiple to a preceding portion in said electric system and including at least one variable, substantially reactive impedance, conpling means'between said plurality of impedance circuits and a succeeding portion of said system for, obtaining differential signal voltages therein, means responsive to current variations, means for energizing said responsive means from said succeeding portion of the system, a coupling between said responsive means and said one variable impedance for controlling the latter from the former at variations of sub-audio-frequency, and adjusting means for another variable impedance, whereby with varying signal strength the signal strength in said succeeding portion will be maintained substantially constant.

5; In an electric system fortransferring signal energy including an electron-tube system," the combination of a plurality of impedance circuits 'for transferring difierential signalvoltages thereto, means responsive to current variations, means for energizing saidresponsivemeans from said succeeding portion of the system, a coupling between said responsive means and said one variable impedance for controlling the latter from the former at variations of sub-audio-frequency, and adjusting means for anothervariable impedance, whereby with varying signal strength the signal strength in said succeeding portion will be maintained substantially constant.

6. In an electric system for transferring signal energy including an electron-tube system, the combination of two impedance circuits connected in multipleito a preceding portion in said electric system, each circuitincluding a condenser and a coil with at least one of said condensers having a variable capacitance, an inductive coupling between said coils and a coil in a succeeding portion of the system for transferring differential signal voltages thereto, means responsive to cur-' rent variations, means for energizing said responsive means from said succeeding portion of the system, accupling between said responsive means and saidone variable condenser for controlling the latter. from the former at variations of sub-audio-fre uency, and adjusting meansfor another variable impedance, whereby with varying signal strength the signal strength in said succeeding "portion will be maintained substantially constant. V

7. In an electric system for transferring signal energyincluding an electron-tube system and a structurefor supplying signal energy thereto, the combination of a plurality of impedance circuits connected in multiple to said signal supply structure and including at least one variable, substantially reactive im'pedancacoupling means between said plurality or impedance circuits and said electron tube system for obtaining differenr tial signal voltagestherein, electric means responsive to current variations, meansfor energizing said electric-means from said electron tube system, a coupling between said electric means and said one variable impedance for controlling the latter from the. formeriat variations of sub-- audio-frequency, and adjusting means for another variable impcdance, whereby with varying signal strength in said supply structure the signal strength in said electron tube system will be maintained substantially constant.

'8. In an electric system for transferring signal energy including an electron-tube system anda structure for supplying signal energy thereto, the

combination of a plurality of impedance circuits connected in multiple to said signal supply structure andzincluding at least one variable, substantially reactive impedance, coupling means between said plurality of impedance circuits and said electron tube systemfor. transferring differential signal voltages thereto, electric means responsive to current'variations, means for en-' ergiz'ing said electric means from said electron tube system, a coupling between said electric means and saidone variable impedance for controlling the latter from the former at variations of sub-audio-frequency, and adjusting means for another variable impedance, whereby with varying signal strength in said supply structure the signal strength in said electron tube system will be maintained substantially constant.

9. In an electric system for transferring signal energy including an electron-tube system and a structure for supplying signal energy thereto, the combination of two impedance circuits connected in multiple to said supply structure, each circuit including a condenser and a coil with at least one of said condensers having a variable capacitance, an inductive coupling between said coils and a coil in said electron tube'system for transferring differential signal voltages thereto, electric means responsive to current variations, means for energizing said electric means from said electron tube system, a coupling between said electric means and said one variable condenser for controlling the latter from the former at variations of sub-audio-frequency, and adjusting means for another variable condenser, whereby with Varying signal strength in said supply structure the signal strength in said electron tube system will be maintained substantially constant.

10. A self-contained volume-control device for supplementing an electric signal current transfer system, said device including an input circuit having accessible connection terminals for abstracting signal energy from a portion of said electric signal system, an output circuit having accessible terminals for transferring signal energy to a succeeding portion of said signal system, a plurality of impedance circuits connected in multiple to said input circuit and including at least one variable, substantially reactive impedance, coupling means between said plurality of impedance circuits and said output circuit for obtaining differential signal potentials in said output circuit, said coupling means having such electrical proportions and coupling relations with respect to each other and the output circuit that for one value of said variable impedance Within its range of variation the transferred diiferential potentials substantially equalize, and adjusting means for said variable impedance whereby the signal energy transferred to said output circuit may be varied from substantially zero value to various desired finite values.

GEORGE E. FLEMING. 

